Telephone-repeater.



V G. D. LINDRIDGE TELEPHONE REPEATER. APPLICATION FILED FEB. 10, 1909.

979,012; Patented Dec.20, 1910.

q UN TED TATES PATENT.

.. cHARLnsn. Lmniiiiien, or PROVIDENCE, mom: isrisivn.

Q rii EPHONE-REPEA ER.

To all whom it may concern: I

Be itknown that I, CHARLns- DJilINDQ described hereinafter isgiven as an example moon, a subject of the King of England, and

a resident of Providence, county of Provi dence, and State of Rhode Island, have invented a new and useful Improvement in Telephone-Repeaters, of ing is a specification. r

My invention relates to systems for the reinforcement of telephone currents wherein means are provided for adding energy to transmission currents without subjecting.

them to the distorting influence of mechani-' cal inertia and momentum.

It particularly relates to reinforcing systems in which negative resistances are made useof at the reinforcing station, and it consists of .an improvement in telephone reinforcing apparatus whereby eater facilities are provided for the appllcation'of the principle involved, by increasing the sensitiveness, uniformity and reliability of the negative resistance, as hereinafter described.

Such systems for the reinforcement of telephone currents rely toa considerable extent for their successful operation upon their ad i justment. Hitherto, in the systems to which this invention particularly relates, 'viz., those which make use ofbreak-down resist-- 'ances, or'mediums which present a-d'ecreas- .ing resistance toacurrent of increasing E. M. F., it has been necessary to rely for satisfactory results upon random adjust ment. That is to say, it has been necessary that the parts of the combinations made use of in these systems be subjected to various unknown relationships until an acceptable one can be found. Considerable difiiculty is presented and uncertainty experienced by this'means;

, My'invention consists of an improvement in these systems wherein the essentialparts v of the combination are subjected to and maintained in a definite and predetermined relationship, thereby making the applica' tionof the system less diflicult and'provid- 3 in anent.

A source of direct current in combination with an induction'coil and aconducting medium having the characteristic of presenting a decreas1ng resistance to a current of -which the follow scribers "stations, and G across the medium "E is. increase creased, according to whether the induced and form a part -of this specification. The combinatlon shown in thesedrawings and of those to which my invention may be applied.

v Specification ofLetters Patcnt- PatentmlDc, :20, 1910, Appfieati on'fled February m, 1909; Serial Ne. 477,091,

in, is intended 'to describe the apparatus. which isusedto increase the power of the,

voice currents. This term'is used irrespective of whether thetelephone currents are renewed,lor renewed and reinforced, or remforcedonly. u

Inithe drawings, A and-B represent subrepresents the reinforcing. station. I g

Referringrto Fig. 1- theoperation-is as follows: The FcurrentS received at 'the induc- Whieh cause the potential across-the conduct otentialing medium E to be varied; The

or de- E. M. F.s oppose or reinforce the E. M. F. of'the'battery D; When a current is inducedlin thewinding --I of the induction coil F-in the-same direction as the current passingv through the circuit 1) E J I; the potential across E is increased. Aszthe resistance of the circuit D E J I is thereby reducedydue to the resistance-varying action at E, a current is-induced in the winding K of the induction coil G which is partly directly due to induction from A and partly caused by a change in the negative resistance of the circuit I) E J I. The resistance of the circuit E J I is changed in the same way when currents are transmitted from B to A.

Before considering the character of nega-v tiveresistance, consideration may be given to resistance which is not negative in character, but which, similar to the negative re sistance in telephone repeaters, is subject to variations .inresistance corresponding to sound Waves. The resistance of a telephone transmitter when the transmitter is spoken into, varies in a similar manner to that in which negative resistance varies when a varying current is passed through it. vThe resistance of telephone transmitters and the negative resistance. in telephone repeaters, are also similar in the respect that they have both hitherto been adjusted in the same manner.

K When a telephone transmitter falls out. of adjustment from any cause, it is the prac- .tice in re-adjusting it, to transmit, or to attempt to transmit speech through it before altering its resistance, so that an idea may be obtained of the extent to which its resistance must be varied, in order to put it into proper working order. Its resistance is then varied, and a second attempt is made to transmit speech through it. If, when its resistance is increased the transmission is made worse, its resistance is decreased, and made less and less, until any further decrease in resistance is found not to improve, but to impair transmission. Its resistance is then left unchanged and the transmitter is in Working order.

\Vhen telephone repeaters wherein negative resistance is used have hitherto been constructed, it has been the practice of those skilled in the art to make such adjustment in like manner. Thenegative resistance has been subjected to variations in adjustment While telephone currents have been transmitted through the repeater. The result of these variations has been noted and used as a guide as to what further adjustment should be made. This method of ad justment is satisfactory for all telephone apparatus which requires adjustment, ex cept negative resistance in telephone 'repeaters. The fact that this method of adjustment is not the most suitable for negative resistance'in telephone repeaters has hitherto laid hidden from vision, and it is upon this fact that this invention is based. The. fact that the conductance of negative resistance varies when a current passing through it varies, .is known; but it has not been realized that because of this character telephone repeaters wherein negative resistance' is used, should be constructed in such manner that the adjustment of the'negative resistance is made in a different manner to that in which the adjustment of other telephone apparatus is made. The reason why they should be constructed in this manner, may be more readily perceived, after considering the manner in which they are constructed when use is made of this invention. The nature of the conducting medium made use of in these systems, which may be made to present a varying resistance to a battery and the transmission currents, may be such as to be dependent for its operation upon thermo-eleqtric action or polarization. A polarized conductor, to have the required characteristic, must of course be subjected to an E. M. F. sufficiently. great tobreak down its efi'ective resistance. Besides these there are other groups of conductors which may be used. For example, those consisting essentially of electrodes differing either in size, form, material or in the nature or denthat all asymmetrical conductors have the characteristic of presenting a decreasing resistance to a current of increasing E. M. F.

Mediums of the character which depend for their operation 'upon either thermo-electric action or polarization are dealt with in the Bullet-in 0f the United States Bureau of Standards, No. 2, Vol. 2, in the article, On the Platinum Point Electroyltic Detector for Electrical aves, by L. W. Austen. In same subsequent investigations made by Mr. Austen upon the silicon detector, tests were made which show this medium to be of the I required character for use to be made thereof ]11' these systems. These mvestigations are described. 111 a letter written to the editors of the Electrical World and published at New York in that publication, Vol. 51, No. 3, dated January 18, 1908. This type of medium is readily endowed with the required degree of sensitiveness, but it would appear that mediums dependent for their operation entirely upon thenno-electric action or polarization are in some respects bettor suited for use in these systems. A method of constructingthe silicon detector will however be described as the results obtained'from its use have been satisfactory.

The silicon in granulated form may be more easily handled when embedded in solder. A convenient method of holding it is by means of a tool-makers in vise, a drop of heated solder and flux belng allowed to fall into a tray of granulated silicon,'i-'and the mass so formed held in the teeth of the vise.- tally in some form of metal mounting to which a binding post is attached.

A micrometer head of the type constructed for use in calipers, measuring to one-thou The vise may be supported horizonabove, the point of contact may be readily changed. A numberof such sets however, considerably m excess of the number intended for use at one time, should be pro- .vided and subjected to constant adjustment,

in order that those most suitable for use may be selected.

It will be observed that a number of contacts may be groupedztogether to produce a greater variation of resistance than may be produced by a single contact. If it is desired that theresistance of the group be the same as the resistance of a single contact, it is necessary to use four contacts, two strings each with two contacts in series, in order that the 'amount of resistance variation may be approximately doubled. If it is desired to again approximately double this amount sity of surrounding gas. It would appear 1 of resistance variation, it is necessary to use contacts in series. Owing to-the rapidly. increasing number of contacts for. higher degrees of resistance variation, it

may be allowed.

. of the character described herein have, 'put to commercial .use, the foregoing deser-rp tion has been considered necessarytoenable sixteen each with four would not appear desirable that. more than four strings of contacts be used. Thenumher of. contacts. in each string may, however with advantage behigher than'four, providj ing a higher normal resistance of the group As previous to this application nos one skilled in the artto construct a-combination'of thetype'towhichuthis inyentio v may be applied. The improvement 'efiected in these. systems by use of this inventionconsists of adjusting preliminarily to a predetermined degree the E. of the local source of currentand' the resistance of the local circuit,- so that the fluctuations in potential across the electrically controlled resistance medium Will fall within the range towhich the medium is, responsive and to which it is preliminarily adjusted.

Telephone repeaters wherein negative resistance isused, havehithertobeen open to the objection'that the telephone currents have not been subjected to a suflicient degree' of reinforcement. This invention has for its object the use of negative resistance inia condition of greater sensitiveness than hitherto, thereby subjecting the telephone currents to greater reinforcement, by arrangingthe parts of'the repeater as follows:

The resistance which the negative resistance is topresent to thesource of current, and the potentialof current which is to bev presented to the negative resistance, are determined before the rep'eaterparts are'arranged in ac-. cordance' with this :invention. Then if c be taken to represent the electromotive force of the source of-current, 5a to represent the potential of current which is determined to be, that to which the negative-resistance will be subjected, W to represent the resistance of the repeater circuit, and 1",, to represent the resistance which is determined to -be that which the negative re'sistancewill present to the source of current, the circuitis arranged to make For example,=-.the .circuit shown in Fig.

1 may be used t'o'reinforce telephone currents arranged so thatthe electromotive force of the-source of current:6 volts, the predetermined potential; of current subjected :to the negative nesistance= 4 volts, the predetermined resi'sta cef'of the negative resistance::200-ohms' fthe resistance of the circuit=300 ohms.

The fact which ha's laid hidden from vision known to be suitable' fo fillsreinforcement and upon which this invention. is based, is that by constructing the repeater in such mannerlthat the negative ."resistance is sub jected to a potentialwfoii urrent which is e 1;-The negative resistance producing the greatest reinforcement of the telephoneficun" rents ofwhich it is capableof producing, only when it is adjusted to a certain resistance, being at the same time subjected to; a certain potential of current. It .does not produce the greatest reinforcement of the telephone currents of which it is capable of producing, if it is adjusted toany other than '90 the one resistance, regardless of thepotential of current to which it is subjected, orif it Y is subjected to any other than the one poten- .tial o f current, regardless of its resistance. 2."The fact that if the negative resistance is fin aufnoderately sensitive condition, and V the Potential ofcurrent to'which it is "subjected is increased, or if its resistaneeis de- A creased, its sensitiveness 1s lncre'ased up to a certain point where'its character and re s ist- 10C ance suddenlv break down without warning.

3. The difference-between the values of'r v v and r s'uch'as there must necessarily be in a telephoneiepeater, causing a variation in either the resistance of the negative resist- .105

'ance, or the poten'tial'of currentpresented to it,'to produceconsiderablevariation in the- I Other. I I Although these conditioiisdo not make it;

impo'ssibleifor the negativeresistance to 'bej l i adjusted tounknown values'which are such asto cause it to produce the greatest rein-- forcement of thetelephone currents of which it is capableof producing, yet theycdomake it impossible for the negative resistance to be utilized when it is adjusted to unknown values, in its condition of greatest sensitive ness in the artof telephony. They :make

this impossible, owing to the fact thativhen the negative resistance is adjusted to mod erately sensitive condition, there is no means of knowing by any variation exhibited in its character, what variation in its resistance and thepotential of current presented to it should be made, in order to increase-its sensitiveness, and whether the slightestincrease in the potential of current presented to it, or; the slight-est decrease in its resistance, will destroy its character. Consequent'ly' undertheseconditions, there is some uncertainty of operation experienced in ad justing it to even a moderate degree of senpresented to it are predetermined, which may be-done in the following manner: It may be connectedinto a tGStiIlgCIiCillt and adjusted to a high resistance. It may then be subjected to a gradually and constantly increasing potential of current from zero up to a sufficiently high value to break down its.

character-as a negative resistance. A curve may be plotted describing the variations in its conductance throughout this range of potential. Its conductance may then be slightly increased and the same operation performed, a second curve being plotted describing the variations in its. conductance throughout the range of potential at this slightly increased value of conductivity. Its conductance may then be again slightly increased, and so on, until its character breaks down at a potential which is known to be lower than that to'which it should besubjected in the repeater. By this means it is possible to obtain a large number of curves, and when it has been determined what resistance the negative resistance will be adjusted to, the potential to which it should be subjected may readily be found by inspection of the curves. It should be slightly below the potential at which the negative resistance loses its character. The conductance to which it should be adjusted may also be determined by inspection of the curves. It should be such that small i .iriations in the current passing through it, produce large variations in the resistance of the repeater circult. By this means the determined values 1) and 71, may be established;

The value of 7- may be-determined by adding the resistance'of the induction coil windings which are connected to the negative 'resistance to 73... 6 may then be found by solving the above equation.

The curves obtained by the investigation of a single negative resistance, maybe used to determine a desirable resistance at which all negative resistances of the type may be.

1 used, and the potential of current to which they should be subjected when. at this resistance. For example'when a silicon-steel negative resistance (see Bulletin of the.

- United. States'Bureaa of Standards, Vol. 5,

page 133) has been investigated, adesirable resistance at which all silieon-steel'negative resistances may be used, and the potential of the one investigation, providing they do not differ in construction, and that they are. all

throwing others out of adjustment. use of this non-inductive resistance, more,

repeater circuit.

.used under the same conditions. Two or more negative resistances-may be grouped together in a repeater to produce a greater variation in.the resistance of the repeater circuit thaninay be produced by a single negative resistance. 1

A repeater including four negative resistances is shown in Fig. 2 of the drawings.

Referring to this drawing-the negative resista nces E E E and E, are connected in the repeater circuit with the batteries D and D Switches are provided to enable connection to be established between any negative resistance and the adjusting circuit- M N O P, and also to provide means by which a noninductive resistance may be connected across a negative resistance before removing it from the repeater circuit to be adjusted. This non-inductive resistance should approximately equal the resistance to which the negative resistance is adjusted,

and allows one negative resistance to be disconnected from the repeater circuit without By the over, a negative resistance may be removed from the repeater circuit to be re-adjusted if a sufficient number are in use, without seriously'imparing the transmission.

The repeater may be adjusted in the following manner: The two-pole switch of the negative resistance E may be thrown to connect the negative resistance to the adj usting circuit M N O P. This allows current from the battery M to pass through the negative resistance and the niil-ainmeter M A. The potential across the resistance 0 may equal the redetermined potential to which the negative resistance is to be subjected. Means should be provided to allow the resistance 0 to be readily subjected to slight variation in resistance. 0 is shown in Fig. 2 subject to slight increase in resistance, by means of the strap key R. WVhen this key is in its normal position, the nega tive resistance may be adjusted to a resistance which is such as to bring the needle of the mil-animeter to a point on the scale to correspond to the predetermined resistance towhich the negative resistance is to be ad justed. The number of scale divisionsover which the needle moves-when the key is depressed, and when a resistance other than negative is connected at E should be known. If this number is increased sufficiently by the current-varying character of the negative resistance when the key It is depressed,

the two-pole switch may be reversed, thereby connecting the negative resistance into the The circuit through the non-inductive resistance L may then be opened. The negative resistances E E and E may afterward be adjusted in like manner.

In the foregoing description I have shown thereof.

- should-be subjected is .91 volt, the highest.

improvement in telephone transmission. I

will now describe the best mode in which I have contemplated applying the principle I provide shown in Fig. 2 having sixteen-mediums, four strings each with four mediums in series, in placeof the four mediums'E Et E 'viation of}; volt therefrom until-it is'convenient .to re lace it. I use the silicon-steel type of me iu'm described heretofore, the

assage of the current being in the direction rom steel to silicon, and find by investiga-.

t-ion thatthe lowest E. M.- F, to which it resistanceto which it should be adjusted is MOIohms, thehi'ghest E. M; F. to which itshould .be subjected is 1.10. volts, and the lowest resistance to which it-should be adjusted is 100 ohms; I therefore provide at each position L.i n the circuit a non-inductive resistanceof 120 ohms. Lprovide atF and G induction. coils', each having two windings, one of 80'ohms connected to one of the transmission lines, and one of ohms connected to the local circuit. I provide in the testing circuit MN OP a'battery of 100 volts atM, a resistance of 98.8 ohms at N,-

a-resistance of '1. ohm MO, and a resistance of .2 ohm at P.- 'Iprovide at M'A a milammeter of'the portable direct-reading type having a rangeof 50 mil-amperes and 100 scale divisions. I mark a point upon the scale of this mil-ammeter at 7 .14 mil amperes v to show the highest resistance towhichthe medium is adjusted in this particular appli cation of this invention, and another at 10 mil-amperes to show the lowest resistance to. which the medium is adjusted. I provide a strap key and switches as shown in Fig. 2.

I first bring all the resistances L into the circuit D J I, and throw a double pole switch to bring one medium into the testing circuit MN 0 P. The measuring surface of all the mediums before adjustmentwill be out of contact witli the silicon. The. measuring 55 surfaceof this first medium to be adjusted is gradually brou lit to bear upon the silicon until the nee e of the nnl-ammeter is brought up to "within the :ab'ove- .oints ey is four. scale divisions theresist 'ance of the medium'is decreased. A. movement of the needle over 3.7 5 SCfl-lQ'dlVlSlOl'lS may or may: 'not'show a decrease in reslstance of themedium according to whether the needle is a combination of the character- .nearer the highest or lowest point marked upon the scale when the strap'ke'y is up. Greater refinement'in the adjustment of the medium will be obvious after having considered this-specification. If the movement of the needle when the strap key is depressed is considered to be suflicient, the double pole switch is reversed and the resistance L disconnected. If this movement is. not considered sufficient, or if difliculty is experienced in adjusting the medium to a resistance which'will bring the needle of the milamme'ter between the points marked upon the scale, it should be replaced. The same method of testing may be followed with the remaining mediums until sixteen'are connected into the circuit D E J. I. It is of course necessary that they be frequently tested during the time they are in use in order. that the potential normally across each medium may remain unchanged;

It is to beunderstood from the foregoing description that this invention is not limited to any particular type ofmedium, but may be used to effect animprovement in any system making use of. the characteristic of a medium presenting. a decreasing resistance to a current of increasing E. M. F. It is also to vbe understood: that the. particular combination to which the invention is hereinthe invention. Other combinations to which this invention may be applied will readily occur to one skilled in the art. For example,

the windings H I J K of the induction coils F and G, shown inthe drawings, may be wound about a single core, or one (3011 with .three windings only may be'used.v Instead of intersecting the station? A and B, the re-;., info'rcing station maybe connected in series with them, and a coil with only two wind ings be used;

Thereforegwithout limiting myself to the ,use' of any particular combination described I heretofore, what- I claim. as new and desire to secure by United States Letters Patent is:

1. In atelephone repeater, a source of unidirectional currentanda negative resistance cuit; means for impressing incoming-voice currents on said circuit;'means for transcircuit on. an outgoing circuit;' and a non inductive! resistance adapted to be substituted. in said'circuit for said-'ne ative resistance-element, substantially as escribed.

- 2. :In atelephone repeater, a source of uni-' directionalcurrentand a negative resistanceelement included togethe'rin a repeater cirtive resistance having approximately the same resistance as the proper workingresistance of said negative resistance element; and means for substituting said non-inductive resistance in said circuit in place of said negative resistance element.

3. In a telephone repeater, a source of uni directional current and a negative resistance element included together in a repeater circuit; means for impressing incoming voice currents on said circuit; meansfor translating the amplifiedcurrents flowing in said circuit on an outgoing circuit; a testing circuit; means for switching said negative resistance element but of said repeater circuit and into said testing circuit; and means for closing said repeater circuit while said negative resistance is switched onto said testing circuit.

4. In a telephone repeater, a source of unidirectional current and a negative resistance element included together in a repeater circuit; means for impressing incoming voice currents onsa1d circuit; means for translating the amplified currents flowing in said circult on an outgoing circuit; a non-inductive resistance; a testing circuit for said negative resistance element; and means for substituting said non-inductive resistance for said negative resistance element in said repeater circuit when said negative resistance elementis connected with said test circuit.

' 5. In a telephone repeater';'a local circuit;

translating devices in said local circuit; a

plurality of negative resistance elements and a source of direct current connected together in said local circuit;'a plurality of non-inductive resistances; and means for substituting one or more of said non-inductive resistances for one or resistance elements.

6. In a telephone repeater; a local circuit;

translating devices in said local circuit; a

plurality of negative resistance elements and more of said negative means-for substituting one of said non-inductive resistances for one of said negative resistance elements and connecting said negative resistance element with said testing circuit for test and adjustment.

7. In a telephone repeater; a local -circuit containing translating devices; a string of negative resistance elements connected with a battery in said local circuit; a plurality of non-inductive resistances associated with said negative resistances; and means for substituting one of said non-inductive resistances for one of said negative resistances, for the purpose herein described.

8. In a telephone repeater; a local circuit containing translating devices; a source of current in said local circuit; a plurality of strings of negativeresistance elements; said strings of negative resistance elements being connected in multiple in the local circuit inchiding said translating devices; substitute resistances for each of said negative resistances; .and means whereby said substitute resistances may be introduced into said local circuit.

9. In a telephone repeater; a local circuit containing translating devices; a source of current in said local circuit; a plurality of "strings of negative resistance elements; said strings of negative resistance elements being connected in multiple, in the local c1rcu1t including said translating devices; non-inductive resistances for each of said negative resistance elements; a testing circuit; means whereby one or more of said negative resistances may be removed from sald local c1rcuit and introduced into said test circuit;

and means for substituting said non-inductive resistance for said negative resistance in said local c1rcu1t.

10. In a telephone repeater; a local circuit. containing translating devices a plurality of allel relation; non-inductive resistances for' each of said negative resistances; a testing c1rcu1t; means wherebyone or more of sald negative resistancesv may 'be removed from said local circuit and introduced into said .testing circuit; and means for substituting said non-inductive resistance for said negative resistance in said local circuit.

Signed by'me at Providence, county of Providence and State of Rhode Island in the presence of two witnesses, anddated Februmy 1st 1909.

HARLES Witnesses:

GILMAN E. Jorr, SIDNEY E. LINDRIDGE'.

D. LINDRIDGE. 

